The present application is being filed concurrently with U.S. patent application Ser. No. 09/636,244 entitled xe2x80x9cInjection-Molded End Stop for a Slider-Operated Fastener,xe2x80x9d U.S. patent application Ser. No. 09/636,421 entitled xe2x80x9cSlider-Operated Fastener With Spaced Notches and Associated Preseals,xe2x80x9d U.S. patent application Ser. No. 09/637,037 entitled xe2x80x9cMethod of Applying a Slider to a Fastener-Carrying Plastic Web,xe2x80x9d and U.S. patent application Ser. No. 09/637,038 entitled xe2x80x9cMethod and Apparatus for Making Reclosable Plastic Bags Using a Pre-Applied Slider-Operated Fastener,xe2x80x9d all of which are incorporated herein by reference in their entireties.
The present invention generally relates to reclosable plastic bags and, more particularly, to a method and apparatus for guiding a fastener in a bag making machine. As used herein, the term xe2x80x9cbag making machinexe2x80x9d may refer to a form, fill, and seal machine or a machine that makes empty bags.
In one method for making reclosable bags, a continuous fastener is sealed to a moving web of thermoplastic film. The fastener-carrying web is subsequently processed into individual plastic bags. One type of fastener includes a pair of interlocking profiles and a pair of fins/flanges extending from the respective profiles. Sliders are preferably mounted to the fastener at bag-width intervals for engaging and disengaging its profiles in response to movement therealong.
In one technique for installing sliders on the fastener, notches are formed in the fastener at bag-width distances apart. To install a slider on the fastener via a respective notch, the slider is first positioned within the notch, and then the slider is threaded onto an end of the fastener in response to relative movement of the slider and fastener. This installation technique is disclosed in U.S. patent application Ser. No. 09/307,937 (PCOS015) entitled xe2x80x9cZipper and Zipper Arrangements and Methods of Manufacturing the Samexe2x80x9d, filed May 10, 1999, and incorporated herein by reference in its entirety. To form a notch, a short segment of the interlocked profiles and an upper portion of the fins extending from that segment are cut away from the fastener, leaving only a lower portion of the fins bridging opposite sides of the notch. Due to the notches and the mounted sliders, the fastener can be difficult to guide and control when processed through a bag making machine. The fastener tends to twist and distort. For example, when sealing the fastener to the web of plastic film, any distortion in the fastener could cause an uneven seal between the fastener and the web. The uneven seal, in turn, could cause wrinkles in the web and a package that leaks due to unsealed or weakly sealed areas.
Furthermore, to seal the fastener to the web of plastic film, a sealer generates seals between the fastener""s fins and the web. Unless precise operational control is maintained over such variables as the alignment, temperature, pressure, and dwell time of the sealer, the sealer could transfer excessive heat to the fins during the sealing process. Such excessive heat could deform the fins, cause the fins to stick to each other, or even accidentally seal the fins to each other. These fin-related problems are exacerbated if the fins are relatively thin and are composed of compatible materials that readily bond to each other. If the fastener is not located properly to the web, the sealer may miss the fastener or seal a skewed fastener to the web resulting in a nonfunctional fastener in the final package.
To overcome the aforementioned shortcomings, the present invention provides a method and apparatus for guiding a fastener in a bag making machine. The apparatus includes a stationary support, an elongated internal guide, and an slitting mechanism. The elongated internal guide is mounted to the support and positioned within an enclosed space defined by the fastener. The fastener is moved downstream with the internal guide within the enclosed space. The fastener is slit upstream from the support. While the fastener is guided, a sealer may seal the fastener to a moving web of plastic film along a seal adjacent to the internal guide.
As the name suggests, the internal guide helps to guide and control the fastener so that it does not twist or distort while moving downstream through the bag making machine. In addition, the internal guide serves as an effective insulator between fastener portions on opposite sides of the internal guide. While the sealer seals the fastener to the moving web, the sealer will not deform such fastener portions, cause the fastener portions to stick to each other, or accidentally seal the fastener portions to each other. In fact, the internal guide reduces the degree of operational control that must be maintained over such variables as the temperature, pressure, and dwell time of the sealer.